constexpr

Ok, suppose I have this magic template that takes a char array and turns it into a template parameter list. For example: "thing" is translated to list<'t','h','i','n','g'> : template<const char*, size_t> ArrayToList; You use it like this: constexpr char string[] = "this is a test"; typedef ArrayToList<string,14> list; Is there any way to somehow detect the string length implicitly so that all I have to do is: typedef ArrayToList<string> list; Unfortunately, it can't be done: You would like to have a non-type template parameter (the string). Syntactically speaking, the only way to specify a non

I had heard that std::bit_cast will be in C++20, and I am slightly puzzled about the conclusion that implementing it necessarily requires special compiler support. To be fair, the argument I have heard is that the implementation performs a memcpy operation, and memcpy is not typically constexpr , while std::bit_cast is supposed to be, so making std::bit_cast constexpr supposedly requires compiler support for a constexpr -compliant memcpy operation. I was wondering, however, if it was possible to implement a compliant bit_cast (ie, defined behavior, to same extent that using memcpy would have

I'm making my own String View class for learning purposes, and I'm trying to make it 100% constexpr. To test it, I have a member function that returns an hash value. I then construct my string view in a switch statement and call that same member function, if it passes, that member function has fullfiled its purpose. To learn, I'm using / reading / comparing my implementation with Visual Studio 2017 latest update std::string_view , however, I've noticed that, despite swap being marked as constexpr , it does not work, nor in Visual Studio, nor in g++. This is the piece of code that does not work

Hi the following program works with g++ 4.9.2 (Ubuntu 4.9.2-10ubuntu13) but the virtual keyword is required for the function get : //g++ -std=c++14 test.cpp //test.cpp #include <iostream> using namespace std; template<typename T> constexpr auto create() { class test { public: int i; virtual int get(){ return 123; } } r; return r; } auto v = create<int>(); int main(void){ cout<<v.get()<<endl; } If I omit the virtual keyword, I get the following error : test.cpp: In instantiation of ‘constexpr auto create() [with T = int]’: test.cpp:18:22: required from here test.cpp:16:1: error: body of

This question already has answers here : Difference between `constexpr` and `const` (8 answers) Closed 2 years ago . In the "Exploring C++17 and beyond" presentation by Mike Isaacson at one point ( https://youtu.be/-ctgSbEfRxU?t=2907 ) there is question about writing: const constexpr .... vs single const. Mike said that in C++11 constexpr implies const and in C++14 it does not. Is it true? I've tried to find prove for that but I couldn't. I'm not asking about difference between const and constexpr (as a lot of other questions) but about difference in constexpr in two versions of C++ standard.